In a mobile phone, a video conference system, a broadcasting system, or the like, various techniques are known in order to suppress noise included in a sound signal collected by a microphone, or the like (hereinafter also referred to simply as a “microphone”). As noise included in a sound signal, there is, for example, an engine sound of a vehicle that passes by the vicinity of a microphone, an operation sound (stationary noise) of a fan and a motor that are installed in a factory, and the like.
The best known technique, as one of the techniques for suppressing noise, is a technique that suppresses noise by a plurality of sound signals collected using a microphone array including a plurality of microphones. As one of the noise suppression techniques of this kind, a microphone array noise reduction control method is known in which spatial orientation information of sound is directly captured by a microphone array, and update filtering by an adaptive filter is more correctly controlled using the orientation information.
Also, as a noise suppression technique using a microphone array, a technique for suppressing noise based on the phase difference of a plurality of sound signals collected by a microphone array is known, in addition.
Also, as one of related noise suppression techniques, a technique is known for suppressing noise by performing filter processing using a Kalman filter on the sound data in frequency domain, which has been obtained using Fourier transformation. Further, as another related noise suppression technique, a technique is known in which the variation width of an amplitude spectrum is restricted in accordance with the variation direction of the amplitude spectrum obtained by the time-to-frequency transformation, and noise is estimated based on this in order to perform noise suppression.
As examples of related-art techniques, Japanese National Publication of International Patent Application No. 2013-511750, Japanese Laid-open Patent Publication No. 2011-186384, Japanese Laid-open Patent Publication No. 2013-120358, and Japanese Laid-open Patent Publication No. 2008-309955 are known.